Can I use Exchange 5.5 as a POP3 host?

Hello,
I have the POP3 protocol installed and we’re receiving our pop3 through gte.net just fine. Just wondering, though, if I can set up my Exchange 5.5 server as an actual pop3 host (where someone else can use my server as a pop3 host. Also we’d like to give them a vanity domain, as their ISP does not provide that. Can we add an “alias” domain so they can receive their mail through that domain (instead of ours or their ISP). Thanks for any reply.